We are mapping the enzymic fluxes through the key intermediate, pyruvate, in isolated liver and kidney cortex cells. The approach involves the synthesis and use of specifically labelled substrates, and isolation and degradation of products and intermediates. With the aid of a microcomputer, the data are converted to rates in the metabolic pathways. The effects of diet, hormones and drugs in perturbing these rates are then examined, in attempts to localizing their sites of action. In this way, we are exploring the control of the major metabolic pathways of gluconeogenesis, glycolysis, lipogenesis and ureogenesis in liver and kidney cells.